My knowledge on this matter is incomplete so maybe someone else can can fill in the gaps. I agree with you about the evils of DRM and Securom, but from what I remember, the Securom install that comes with Bioshock is not a rootkit as such; it is just a very snidey spiteful type of install which is difficult to remove because it creates registry entries that Windows finds hard to recognise since they contain illegal characters. If you do wish to remove it afterwards, it's just a matter of following one of the step by step guides online (no links to hand I'm afraid). If you are worried about removing it, then it's probably best to check one of these guides before installing it and making sure you're confident of being able to follow the removal steps.
While it's installed, aside from the ignominy of knowing that devs have put something on your PC that you have no control over, you won't notice much of an effect unless you try to run Bioshock after having run some specific programs like Process Explorer (an excellent utility from sysinternals which I use all the time). Securom notices that these blacklisted programs have run and will refuse to let Bioshock run until you restart your machine.
The other effect of their DRM is of course the limited number of installs you can make of the game. If you don't already know, you are only allowed to install the game on a limited number of unique hardware configurations in your lifetime, although from what I understand formatting your comp and then reinstalling will count as a second install, and even uninstalling/reinstalling might count towards the limit(?). From what I remember, Y2K upped the number of installs you are allowed to about 5(?)- by now they might have removed the limit completely (if they have a ****ing brain), but I have no idea. That's the extent of what I know.
yeah, I want to replay the game (I bought it when it came out) but I'm waiting for the patch they promised that will get rid of all that copy protection bullshit
I believe 2K made a program to officially uninstall Bioshock, or at least, repeal one of the 'uses' in the event that you were going to knowingly remove it? So far, none of the DRM schemes for me has caused any more problems than 'hey, turn off Daemon tools or I won't run'. If I am actually still playing the game when I've used up my five (or whatever) installs and need another, and 2K has not done something about this, I may do something irrational.